Smoke detectors and gas detectors have been utilized separately for a number of years. However, until recently, circuitry required for these devices was rather complicated and did not lend itself to low cost consumer use. As a result of increasing market demand, integrated circuits have been developed which integrate a number of functions for smoke alarms onto a single chip. However, certain testing agencies such as Underwriters Labs have put certain restraints on smoke detectors which require certain output functions in order to operate.
When combining a smoke detector with a gas detector, it is still important to reduce the circuitry required for the combined operation of the system. At this point in time, smoke detectors and gas detectors are not commonly found together in an integrated unit. To integrate the functions of two separate devices into a single package would be expensive and difficult to manufacture. Therefore, there exists a need for an integrated smoke and gas detector which combines the output detection and alarm circuitry for both detection modes to reduce the overall amount of circuitry required for operation of the device.